The purposes of the present study are to clarify the resistance mechanisms of housefly to several insecticides using biochemical and genetic analyzes, and to survey and utilize transposon as a transigenic tools in insects. Resistance mechanisms of housefly to pyraclofos, profenofos and permethrin were clarified including insensitivity of AChE,and increased detoxication by P450, esterase and GST at primary metabolism. Glucose-transferase involved in secondary metabolism of profenofos. Results of linkage-analysis indicated that the pyraclofos and pyriproxyfen resistances were controlled by incomplete dominant alleles. Two genes related with pyraclofos resistance were located on 2nd and 5th chromosomes. For the pyriproxyfen resistance, both quantitative and qualitative changes of P450 were detected, and the resistance gene (s) was located on 2nd chromosome. The P450 has been also partially purified and the determination of amino acid seqences is on the way. Two cDNA fragments of housefly AChE were cloned by PCR.In permethrin resistant Culex mosquito, high detoxication by P450 was found to be a major factor of resistance mechanisms. This particular P450 genes could be classified into sixth family. The PCR analysis revailed that the mariner-like element (s) could be reiterated sequences in housefly genome. Homology of the element to mariner was low except primer recognition sites. The mariner-like element seems to loose its function as a transposon. Since the non-functional transposon could be activated by other co-factors, the mariner-like element could be utilized as transgenic tools in housefly.